DESCRIPTION: Deficits in speech perception and language acquisition with relative preservation of pure tone detection thresholds and other elementary psychoacoustic functions are common findings in diseases afflicting the auditory forebrain. Injury to the peripheral auditory system, especially early in development, often leads to central pathophysiological changes and perceptual impairments that cannot be overcome by prostheses or cochlear implants. The present application seeks to continue the development of our nonhuman primate model for analyzing the physiological response properties of auditory cortical neurons in relation to the acoustical features of communication sounds. Specifically, the timing and magnitude of neuronal excitation and inhibition evoked by species-specific vocalizations and synthetic stimuli will be analyzed in alert Macaca mulatta with respect to: 1) the spectral energy distribution and harmonic structure of the stimulus; 2) the temporal envelope of the stimulus waveform; 3) the temporal separation of stimulus events; 4) the temporal order of stimulus events; 5) the acoustic and contextual categories of vocal stimuli; and 6) the spectrotemporal receptive field properties of the neuron. Microelectrode penetrations into posterior superior temporal cortex will be stereotaxically guided using magnetic resonance imaging; recording sites will be reconstructed histologically after terminal mapping experiments, and microanatomical correlates will be defined using acetylcholinesterase, cytochrome oxidase, parvalbumin, Nissl, and myelin staining methods. In the longer term, this experimental model could be developed to investigate central pathophysiological-functional correlates of acute and chronic peripheral disease and to compare cortical neuron responses to vocal communication sounds before and after cochlear implantation. The aim of research on the single-unit physiology of auditory cortex in relation to the psychophysics of vocal communication is to advance basic knowledge about auditory function in the hope of enhancing treatment strategies for communication disorders that utilize electrical stimulation, prostheses, and rehabilitation therapy.